week's boston marathon bombings is responding to investigators questions, marking a dramatic turn for law enforcement officials trying to piece together what was behind that attack. our scott cohn is in boston and has the latest on the investigation. scott, good morning. >> reporter: good morning, carl. it's hard to believe it's been one week since those horrible bombings at the end of the boston marathon. later today at 2:50 local time, the precise time of those bombings one week ago, there will be a moment of silence in boston and church bells will toll throughout the city. dzhokhar tsarnaev, the 19-year-old bombing suspect remains in serious condition where he is recovering from his wound, but apparently he is alert enough to begin responding to some of the investigators' questions. many of those responses in writing because he has gunshot wound possibly, self-inflicted to the throat, but amazingly, he and his brother for some three days managed to hide in plain sight. dzhokhar at umass dartmouth where he was a student, he worked out in the gym, even talked to friends about the bombing